I. Field of the Invention
The present invention relates generally to the fields of biology and medicine. More particularly, it concerns compounds and methods for the treatment and prevention of diseases such as those associated with oxidative stress and inflammation.
II. Description of Related Art
Many serious and intractable human diseases are associated with dysregulation of inflammatory processes, including diseases such as cancer, atherosclerosis, and diabetes, which were not traditionally viewed as inflammatory conditions. Similarly, autoimmune diseases such as rheumatoid arthritis, lupus, psoriasis, and multiple sclerosis involve inappropriate and chronic activation of inflammatory processes in affected tissues, arising from dysfunction of self vs. non-self recognition and response mechanisms in the immune system. In neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, neural damage is correlated with activation of microglia and elevated levels of pro-inflammatory proteins such as inducible nitric oxide synthase (iNOS).
One aspect of inflammation is the production of inflammatory prostaglandins such as prostaglandin E, whose precursors are produced by the enzyme cyclo-oxygenase (COX-2). High levels of COX-2 are found in inflamed tissues. Consequently, inhibition of COX-2 is known to reduce many symptoms of inflammation and a number of important anti-inflammatory drugs (e.g., ibuprofen and celecoxib) act by inhibiting COX-2 activity. Recent research, however, has demonstrated that a class of cyclopentenone prostaglandins (e.g., 15-deoxy prostaglandin J2, a.k.a. PGI2) plays a role in stimulating the orchestrated resolution of inflammation. COX-2 is also associated with the production of cyclopentenone prostaglandins. Consequently, inhibition of COX-2 may interfere with the full resolution of inflammation, potentially promoting the persistence of activated immune cells in tissues and leading to chronic, “smoldering” inflammation. This effect may be responsible for the increased incidence of cardiovascular disease in patients using selective COX-2 inhibitors for long periods of time. Corticosteroids, another important class of anti-inflammatory drugs, have many undesirable side effects and frequently are not suitable for chronic use. Newer protein-based drugs, such as anti-TNF monoclonal antibodies, have proven to be effective for the treatment of certain autoimmune diseases such as rheumatoid arthritis. However, these compounds must be administered by injection, are not effective in all patients, and may have severe side effects. In many severe forms of inflammation (e.g., sepsis, acute pancreatitis), existing drugs are ineffective. In addition, currently available drugs typically do not have significant antioxidant properties, and are not effective in reducing oxidative stress associated with excessive production of reactive oxygen species and related molecules such as peroxynitrite. Accordingly, there is a pressing need for improved therapeutics with antioxidant and anti-inflammatory properties.
A series of synthetic triterpenoid analogs of oleanolic acid have been shown to be inhibitors of cellular inflammatory processes, such as the induction by IFN-γ of inducible nitric oxide synthase (iNOS) and of COX-2 in mouse macrophages. See Honda et al. (2000a); Honda et al. (2000b), and Honda et al. (2002), which are all incorporated herein by reference. For example, one of these, 2-cyano-3,12-dioxooleane-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me), is currently in clinical trials for a variety of disorders related to inflammation, including cancer and diabetic nephropathy. The pharmacology of these molecules is complex, as they have been shown to affect the function of multiple protein targets and thereby modulate the function of several important cellular signaling pathways related to oxidative stress, cell cycle control, and inflammation (e.g., Dinkova-Kostova et al., Ahmad et al., 2006; Ahmad et al., 2008; Liby et al.). Given that the biological activity profiles of the known oleanolic acid derivatives vary, and in view of the wide variety of diseases that may be treated with compounds having potent antioxidant and anti-inflammatory effects, it is desirable to synthesize new candidates for the treatment or prevention of disease.